Display area slides after pagenation enabled while list runnning.

[TSUBOI Shotaro]

Describe the bug
I added items to list while list model running.
Then, display area slides 1 line to upper.
Selected item (or once selected items) is displayed properly.

Setup
Please complete the following information along with version numbers, if applicable.

• WSL on Windows11
• fish and bash
• Windows terminal
• en_US.UTF-8

To Reproduce
I little modify bubbletea/example/list-sample/main.go.
This program appends items each 1 seccond.
When items overflow a page, the display area slides.

Source Code
This not run on go playground.
https://go.dev/play/p/RLjPz27-lxx

Expected behavior
Display area will not slide, and index will saved each additions.

Screenshots

[TSUBOI Shotaro]

additional comments

• I think list.AppendItems API may be needed for efficiency.
• Is the list module assumed that able to append items additionally by design? (what use cases does SetItems API envision?)

[naglis]

IIUC there is a bug here when SetItems() (or other method which modifies items and calls updatePagination()) would result in the pagination being shown (or hidden, if items are being removed?), we subtract pagination height from availHeight using current paginator state and paginator's PerPage and TotalPages are only updated afterwards:

bubbles/list/list.go

Lines 745 to 751 in 95d7be5

 m.Paginator.PerPage = max(1, availHeight/(m.delegate.Height()+m.delegate.Spacing())) 
  
 if pages := len(m.VisibleItems()); pages < 1 { 
 	m.Paginator.SetTotalPages(1) 
 } else { 
 	m.Paginator.SetTotalPages(pages) 
 } 

So, e.g. if we already have 5 items in the list and have height available for 5 items (pagination is currently not shown) and then do SetItems(...) with 6 items (which would cause pagination to be shown), we would only subtract 1 (paginationView() height when there is only one page) instead of 2 (paginationView() height when there are more pages - it has an extra margin of 1) here because paginator per page/total pages is only updated later, so we assume we have more height than we actually have.

[shun]

As a workaround, it seems that setting the correct height can be achieved by executing m.list.SetHeight(m.list.Height()) after cmd := m.list.SetItems(listItems). Here, m is tea.Model, and m.list is list.Model.